Bullhead...Hydrated lime used correctly is the cheapest and most effective way to sterilize a pond basin.

The pond can be re-stocked within a day or two... It is the extremely high Ph and shock that kills. Normally a pond is lowered as much as possible and the lime is applied heavily on all wet areas and the remaining pool area. As the pond refills, the H lime is diluted, but even if applied to a full pool (expensive), the chemical reaction "peters out" as you say in 2-4 weeks on average.

Fwiw, I began offering a guaranteed pond sterilization service this year for those not comfortabe or capable of doing it themself.